Illumination system of a microlithographic projection exposure apparatus

Abstract

An illumination system of a microlithographic projection exposure apparatus includes a pupil forming unit directing light on a spatial light modulator that transmits or reflects impinging light in a spatially resolved manner. An objective images a light exit surface of the spatial light modulator on light entrance facets of an optical integrator so that an image of an object area on the light exit surface completely coincides with one of the light entrance facets. The pupil forming unit and the spatial light modulator are controlled so that the object area is completely illuminated by the pupil forming unit and projection light associated with a point in the object area is at least partially and variably prevented from impinging on the one of the light entrance facets.

What is claimed is: 
     
       1. An illumination system, comprising:
 an optical integrator configured to produce a plurality of secondary light sources in a pupil plane, the optical integrator comprising a plurality of light entrance facets, each light entrance facet being associated with one of the secondary light sources, images of the light entrance facets being at least substantially superimposed in a mask plane; 
 a spatial light modulator having a light exit surface, the spatial light modulator configured to transmit or to reflect projection light in a spatially resolved manner; 
 a pupil forming unit configured to direct projection light onto the spatial light modulator; 
 an objective configured to image the light exit surface of the spatial light modulator onto the light entrance facets of the optical integrator so that an image of an object area on the light exit surface has the same shape and size as one of the light entrance facets; and 
 a control unit configured to control the pupil forming unit and the spatial light modulator so that: i) the object area is completely illuminated by the pupil forming unit; and ii) projection light associated with a point in the object area is at least partially and variably prevented from impinging on the one of the light entrance facets. 
 
     
     
       2. The illumination system of  claim 1 , wherein the pupil forming unit comprises a first beam deflection array of first reflective or transparent beam deflection elements, and each beam deflection element is configured to illuminate a spot on the spatial light modulator at a position that is variable by changing a deflection angle produced by the beam deflection element. 
     
     
       3. The illumination system of  claim 2 , wherein, during use of the illumination system, the light spots produced by the first beam deflection elements on the object area are larger than the object area. 
     
     
       4. The illumination system of  claim 1 , wherein the spatial light modulator comprises a second beam deflection array of second reflective or transparent beam deflection elements, and each second beam deflection element has: i) a first state configured to direct impinging light towards the optical integrator; and ii) a second state configured to direct impinging light elsewhere. 
     
     
       5. The illumination system of  claim 4 , wherein the second beam deflection array comprises a digital mirror device. 
     
     
       6. The illumination system of  claim 4 , wherein at least 10 second beam deflection elements are arranged in the object area. 
     
     
       7. The illumination system of  claim 4 , wherein centers of adjacent second beam deflection elements arranged in the object area are aligned along a straight line, an image of the straight line forms an angle α to a boundary line of the one of the light entrance facets, α is distinct from m·45°, and m=0, 1, 2, 3, . . . . 
     
     
       8. The illumination system of  claim 7 , wherein boundaries of the second beam deflection elements are arranged in a first rectangular grid, boundaries of the light entrance facets are arranged in a second rectangular grid, and an image of the first rectangular grid formed on the light entrance facets forms the angle α to the second rectangular grid. 
     
     
       9. The illumination system of  claim 4 , wherein a length of the object area along a first direction is greater than a length of the object area along a second direction which is orthogonal to the first direction, the objective is an anamorphotic objective having a magnification M, and |M| is less along the first direction than along the second direction. 
     
     
       10. The illumination system of  claim 9 , wherein the second direction corresponds to a scan direction along which the mask moves while the mask is illuminated by the illumination system during use of the illumination system. 
     
     
       11. The illumination system of  claim 4 , wherein the second beam deflection elements are arranged in an object plane of the objective that is parallel to a plane in which the light entrance facets are arranged, and during use of the second beam deflection elements produce in the first state a deflection of impinging light by an angle distinct from zero. 
     
     
       12. The illumination system of  claim 4 , wherein the second beam deflection elements are arranged in an object plane of the objective that is parallel to a plane in which the light entrance facets are arranged, the objective is non-telecentric on an object side, and the objective is telecentric on an image side. 
     
     
       13. The illumination system of  claim 4 , further comprising a scattering plate in a light path between the optical light modulator and the mask plane. 
     
     
       14. The illumination system of  claim 1 , wherein at least one half of all object areas on the light exit surface of the spatial light modulator are completely illuminated by the pupil forming unit during use of the illumination system. 
     
     
       15. The illumination system of  claim 1 , wherein the object area on the light exit surface of the optical light modulator is an active object area configured to prevent projection light associated with a point in the active object area from impinging on the one of the light entrance facets, and the spatial light modulator has another object area that is a passive object area configured to avoid preventing projection light associated with a point in the passive object area from impinging on the one of the light entrance facets. 
     
     
       16. The illumination system of  claim 15 , wherein, during use of the illumination system, the irradiance produced on the spatial light modulator by the pupil forming unit is higher on the active object area than on the passive object area. 
     
     
       17. The illumination system of  claim 15 , wherein the passive object area and the active object area are arranged point-symmetrically to each other with respect to an optical axis of the illumination system. 
     
     
       18. The illumination system of  claim 17 , wherein the optical light modulator comprises a plurality of active object areas and a plurality of passive object areas, and each passive object area is arranged point-symmetrically to one of the active object areas. 
     
     
       19. The illumination system of  claim 18 , wherein the objective comprises:
 a first array of first optical elements, each first optical element configured to form a magnified image of one of the groups in an intermediate image plane; and 
 imaging optics configured to image the intermediate image plane on the light entrance facets. 
 
     
     
       20. The illumination system of  claim 1 , wherein the light exit surface of the optical light modulator comprises groups of object areas that are separated by areas that are not imaged on the light entrance facets, and the objective is configured to combine images of the object areas so that the images of the object areas abut on the optical integrator. 
     
     
       21. The illumination system of  claim 1 , wherein the image of the object area on the light exit surface has the same orientation as the one of the light entrance facets. 
     
     
       22. A method, comprising:
 producing an irradiance distribution of projection light on a spatial light modulator that has a light exit surface and is configured to transmit or reflect projection light in a spatially resolved manner, the light exit surface comprising an object area that is completely illuminated by projection light; 
 imaging the object area on the light exit surface on a light entrance facet of an optical integrator so that an image of the object area has the same shape and size as the light entrance facet; and 
 controlling the spatial light modulator so that projection light associated with a point in the object area is at least partially prevented from impinging on the light entrance facet. 
 
     
     
       23. The method of  claim 22 , wherein the image of the object area has the same orientation as the light entrance facet. 
     
     
       24. An illumination system, comprising:
 an optical integrator configured to produce a plurality of secondary light sources in a pupil plane, the optical integrator comprising a plurality of light entrance facets, each light entrance facet being associated with one of the secondary light sources; 
 a spatial light modulator having a light exit surface, the spatial light modulator configured to transmit or to reflect impinging projection light in a spatially resolved manner; 
 a pupil forming unit configured to direct projection light on the spatial light modulator; 
 an objective configured to image the light exit surface of the spatial light modulator onto the light entrance facets of the optical integrator so that an image of an object area on the light exit surface has the same shape and size as one of the light entrance facets; and 
 a control unit configured to control the pupil forming unit and the spatial light modulator so that the object area is completely illuminated by the pupil forming unit. 
 
     
     
       25. The illumination system of  claim 24 , wherein the image of the object area on the light exit surface has the same orientation as the one of the light entrance facets. 
     
     
       26. An illumination system, comprising:
 a pupil forming unit configured to direct light on a spatial light modulator that is configured to transmit or to reflect impinging light in a spatially resolved manner; 
 an objective configured to image a light exit surface of the spatial light modulator onto light entrance facets of an optical integrator so that an image of an object area on the light exit surface has the same shape and size as one of the light entrance facets; and 
 a control unit configured to control the pupil forming unit and the spatial light modulator so that: i) the object area is completely illuminated by the pupil forming unit; and ii) projection light associated with a point in the object area is at least partially and variably prevented from impinging on the one of the light entrance facets. 
 
     
     
       27. The illumination system of  claim 26 , wherein the image of the object area on the light exit surface has the same orientation as the one of the light entrance facets.